Run the testcase below. You'll see a Frame with an owned Window. Try to click
the Window's button with the SPACE. Then click the Frame and return back to the Window.
Now the Window's button can't be activated with the keyboard.

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import java.awt.*;
 
public class Test {
    static Frame frame = new Frame("Test Frame");
    static Window window = new Window(frame);

    static Button frameButton = new Button("button");
    static Button winButton = new Button("button");
 
    public static void main(String[] args) {
        frame.setBounds(0, 0, 200, 200);
        frame.add(frameButton);

        window.setBounds(300, 0, 160, 160);
        window.add(winButton);

        frame.setVisible(true);
        window.setVisible(true);
    }
}
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